Stabilization of a multi-channel optical signal transmitter through correlation feedback

Abstract

Methods and apparatus for stabilizing or otherwise controlling optical signal power levels in a multi-channel optical communication system. A multi-channel optical signal is detected in a single receiver, and the resulting detected signal is supplied to a correlator. The correlator correlates the detected multi-channel signal with a data signal associated with a particular channel to be controlled in order to generate a measure of the optical signal power of the particular channel. The measure is utilized in a feedback control loop to control an optical signal power level of the particular channel. The correlator may generate the measure of optical signal power by mixing the detected signal and the data signal in an RF mixer, by multiplying the detected signal and a data signal in the form of a unique identifier associated with the particular channel, or by using other suitable correlation techniques. A feedback control processor may be used to process the measure to generate a control signal which is applied to a current source generating current for the particular channel in a multi-frequency laser or other multi-channel optical source. The processor may sequentially monitor and control each of the multiple channels of the multi-channel optical signal using the same receiver and correlator.

What is claimed is: 
     
       1. A method of controlling optical signal power level in an optical system, the method comprising the steps of: correlating a detected multi-channel optical signal with a data signal which modulates a particular channel of the multi-channel optical signal in order to generate a measure of the optical signal power of the particular channel; and   utilizing the measure to control an optical signal power level of the particular channel.   
     
     
       2. The method of claim 1 wherein the step of utilizing the measure to control a power level in the channel further includes the step of supplying the measure as a feedback signal to a feedback control processor. 
     
     
       3. The method of claim 2 wherein the feedback control processor generates a control signal which is applied to a current source associated with the particular channel in order to adjust the optical signal power level of the channel. 
     
     
       4. The method of claim 1 wherein the step of correlating a multi-channel optical signal with a data signal associated with a particular channel further includes the step of applying a detected version of the multi-channel optical signal and the particular channel data signal to respective first and second inputs of a mixer. 
     
     
       5. The method of claim 4 wherein the first and second inputs of the mixer correspond to respective RF and LO inputs of the mixer. 
     
     
       6. The method of claim 1 wherein the step of correlating a multi-channel optical signal with a data signal of a particular channel to generate a measure of the optical signal power of the particular channel further includes the step of correlating the multi-channel optical signal with a data signal in the form of a unique channel identifier associated with the particular channel. 
     
     
       7. The method of claim 6 wherein the step of correlating the multi-channel optical signal with a data signal in the form of a unique channel identifier associated with the particular channel further includes the step of multiplying the multi-channel optical signal and the unique channel identifier. 
     
     
       8. The method of claim 6 wherein the unique channel identifier is configured to include an equal number of values of each of two logic levels. 
     
     
       9. The method of claim 6 wherein unique channel identifiers associated with each of a plurality of channels of the multi-channel signal are configured such that the identifiers correspond to a set of orthogonal vectors. 
     
     
       10. An apparatus for controlling optical signal power level in an optical system including a multi-channel optical signal source, the apparatus comprising: a correlator having a first input connected to receive a detected multi-channel optical signal generated by the multi-channel optical signal source, and a second input connected to receive a data signal which modulates a particular channel of the multi-channel optical signal wherein the correlator is operative to correlate the detected multi-channel optical signal and the particular channel data signal in order to provide an output corresponding to a measure of the optical signal power of the particular channel; and   a feedback control processor having an input connected to receive the measure from the correlator, and operative to utilize the measure to control an optical signal power level of the particular channel.   
     
     
       11. The apparatus of claim 10 wherein the feedback control processor is operative to utilize the measure to generated control signal which is applied to an input of a current source supplying current to the multi-channel signal source. 
     
     
       12. The apparatus of claim 10 wherein the correlator further comprises a mixer having a first input connected to receive the detected multi-channel optical signal and a second input for receiving the particular channel data signal. 
     
     
       13. The apparatus of claim 12 wherein the first and second inputs of the mixer correspond to respective RF and LO inputs of the mixer. 
     
     
       14. The apparatus of claim 10 wherein the correlator is operative to correlate the detected multi-channel optical signal with a data signal by multiplying it with a data signal in the form of a unique channel identifier associated with the particular channel. 
     
     
       15. The apparatus of claim 14 wherein the unique channel identifier is configured to include an equal number of values of each of two logic levels. 
     
     
       16. The apparatus of claim 14 wherein unique channel identifiers associated with each of a plurality of channels of the multi-channel signal are configured such that the identifiers correspond to a set of orthogonal vectors. 
     
     
       17. An optical system comprising: a multi-channel optical signal source;   a receiver having an input coupled to an output of the signal source, the receiver detecting a multi-channel optical signal generated by the multi-channel optical signal source;   a correlator having a first input connected to receive a detected multi-channel optical signal from the receiver, and a second input connected to receive a data signal which modulates a particular channel of the multi-channel optical signal, wherein the correlator is operative to correlate the detected multi-channel optical signal and the particular channel data signal in order to provide an output corresponding to a measure of the optical signal power of the particular channel; and   a feedback control processor having an input connected to receive the measure from the correlator, and operative to utilize the measure to control an optical signal power level of the particular channel.   
     
     
       18. The system of claim 17 wherein the feedback control processor is operative to utilize the measure to generate a control signal which is applied to an input of a current source supplying current to the multi-channel signal source. 
     
     
       19. The system of claim 17 wherein the correlator further comprises a mixer having a first input connected to receive the detected multi-channel optical signal and a second input for receiving the particular channel data signal. 
     
     
       20. The system of claim 17 wherein the correlator is operative to correlate the detected multi-channel optical signal with a data signal by multiplying it with a data signal in the form of a unique channel identifier associated with the particular channel. 
     
     
       21. The system of claim 20 wherein the unique channel identifier is configured to include an equal number of values of each of two logic levels. 
     
     
       22. The system of claim 20 wherein unique channel identifiers associated with each of a plurality of channels of the multi-channel signal are configured such that the identifiers correspond to a set of orthogonal vectors.